Left ventricular (LV) ejection fraction at rest is an important determinant of long-term prognosis in patients with aortic regurgitation. To assess the prognortic implications of the LV ejection fraction during exercise, we studied 70 initially asymptomatic patients by serial radionuclide angiography, of whom 11 developed symptoms requiring operation during followup. These data indicate that 1) LV ejection fraction decrease during exercise compared to the value at rest early in the course of aortic regurgitation, including 90% of patients with echo LV systolic dimension more than 40 mm; 2) initial exercise ejection fraction does not predict either development of symptoms nor deterioration in rest ejection fraction; and 3) depressed preop exercise ejection fraction in symptomatic patients improves postop. Hence, the exercise ejection fraction has unproven prognostic vaue and should not be used alone in determining timing of operation in asymptomatic patients.